1. Field of the Invention
The present invention relates to an underwater riprap foundation and a consolidation smoothing method therefor.
2. Description of the Related Art
Conventionally, an underwater riprap foundation consolidation smoothing method of the weight free fall type is known and used for construction of a mole, a quay or the like. According to the underwater riprap foundation consolidation smoothing method, ripraps are thrown into the water so as to be piled up under the water to form an underwater riprap foundation having a trapezoidal transverse section and a height greater by a required extra-banking height than a planned height for the top end. Further, free fall of a weight is carried out repetitively to consolidate and smooth the underwater riprap foundation to the planned top end height. The underwater riprap foundation consolidation smoothing method is disclosed, for example, Japanese Patent No. 2,893,527 (hereinafter referred to as Patent Document 1) and Japanese Patent No. 3,284,348 (hereinafter referred to as Patent Document 2).
According to the consolidation smoothing described above, within a region of a horizontal portion of the underwater riprap foundation within which a structure such as a caisson which applies a high load is to be supported, in order to prevent possible settlement of the structure by an earthquake or waves, it is necessary to raise the degree of consolidation to sufficiently engage the ripraps with each other until the porosity becomes lower than a fixed level and to finish the underwater riprap foundation with a high degree of accuracy such that the dimensional error of the planned top end height falls within an allowable range of approximately ±5 cm. However, within another range of the same horizontal portion within which only mulch blocks or like elements which provide a low load are to be supported, there is no problem even if the consolidation degree is lower than that where the region in which the load is high, and an error of approximately ±30 cm is permitted. Further, for a face of slope, also an error of approximately ±50 cm is permitted.
However, since conventionally an entire underwater riprap foundation is consolidated to a degree substantially equal to that required for a region in which the load is high and is smoothed to an accuracy substantially equal to that required for the region in which the load is high, also within a region within which the load is low and a face of slope, the underwater riprap foundation is consolidated to an excessively high degree of consolidation and smoothed to an excessively high degree of accuracy uselessly. Thus, the execution efficiency is low and also the cost for construction is high.
Further, that an underwater riprap foundation includes a portion in which ripraps are consolidated to an excessively high degree of consolidation so as to be smoothed to a planned top end height as described above signifies that an excessive amount of ripraps is consumed, which apparently is uneconomical.
Further, since conventionally the extra-banking height is set equal over the overall underwater riprap foundation, when consolidation smoothing in a certain region is to be performed using a weight, ripraps are sometimes forced up to an adjacent region within which the consolidation smoothing is completed already, resulting in the necessity to carry out the consolidation smoothing in the adjacent region again. Also in this regard, the conventional consolidation smoothing is low in efficiency.